The present invention relates to an electrode connection structure to connect a group of external lead-out electrodes of a flat device and a group of output electrodes of a film carrier on which semiconductor devices to drive the flat device are installed in a flat display device such as a liquid crystal display device, a plasma display device, an EL display device, or the like, and in a flat device such as a sensor array or the like such as a one-dimensional image pickup device, a photo detector, or the like.
A conventional technology will now be described using a flat display device.
To drive a flat display device, a group of external lead-out electrodes of the display device are needed to be connected to a group of output electrodes of a circuit substrate on which driving semiconductor devices are installed, and a few methods have been used for this purpose of connection.
For example, as shown in FIG. 2, to connect a group of output electrodes formed at the end of a circuit substrate 2 in which a plurality of driving semiconductor devices 1 are installed on the same substrate with a group of external lead-out electrodes 4 of a display device 6, an anisotropic conductive rubber 5 in which conductive portions and nonconductive portions are alternately arranged is interposed between both of those groups of electrodes and pressed so as to be come into contact therewith. As shown in FIG. 3, a flexible circuit substrate 2 for connection is used and the group of output electrodes of the circuit substrate 2 and a group of external lead-out electrodes of a flat display device 3 are thermally fused and adhered by way of the flexible circuit substrate for connection using a solder or the like or thermally pressed and adhered by way of an adhesive agent and an anisotropic conductive film formed from a conductive dispersing agent. As another example, as shown in FIG. 4, there is a method whereby the semiconductor devices 1 for driving are installed on the flexible circuit substrate 7 and a group of output electrodes formed at one end of the substrate 7 and a group of external lead-out electrodes of the display device 3 are connected by way of either one of the above-mentioned methods.
The foregoing methods have several problems, respectively.
(1) In the method using the anisotropic conductive rubber, the internal resistance is so high (over tens of ohms) that the electrical loss increases.
(2) In the thermal fusion and adhesion using a solder or the like, processing steps (plating and evaporation) of the electrode surfaces of the display device are needed, so that the steps become complicated and also only a limited electrode material can be used and the electrodes which have once been connected cannot be replaced.
(3) The anisotropic conductive film uses a resin as an adhesive material, so that heat resistance and moisture resistance are bad and a reliability remarkably deteriorates.
(4) For the flexible circuit substrate, the film serving as a base material of the substrate thermally contracts, so that a deviation in pitch occurs in the case where it is used for a display device with a narrow pitch and a large picture plane.